Electron contribution to photon transport in coupled photon-electron problems: inner-shell impact ionization correction to XRF

The Monte Carlo code PENELOPE (coupled electron-photon Monte Carlo) has been used to compute the effect of the secondary electrons on the X-ray fluorescence characteristic lines. The mechanism that produces this contribution is the inner-shell impact ionization. The ad hoc code KERNEL (which calls the PENELOPE library) has been used to simulate a forced first collision at the origin of coordinates. The electron correction (produced by the secondary electrons and their multiple scattering) has been studied in terms of angle, space and energy. The energy dependence has been quantified in the interval 1-150keV, for all the emission lines (K, L and M) of the elements with atomic numbers Z=11-92. For each characteristic line, the energy dependence is described by simple parametric expressions corresponding to the five energy regions delimited by the K, L1, L2 and L3 absorption edges. It has been introduced a new photon kernel comprising the correction due to inner-shell impact ionization. The new kernel is suitable to be adopted in photon transport codes (either deterministic or Monte Carlo) with a minimal effort. Finally, the new kernel has been studied for different elements and lines to trace a general behavior.